NSW in January 2012: Wettest January since 1996

Rainfall

NSW recorded a statewide average of 87.7 mm during January, above the historical average of 67.3 mm and the 15th wettest on record. This was slightly wetter than the 84.5 mm recorded in January 2011, making this the wettest January since 1996. The above average rainfall followed similar falls during November and December, and was associated with a La Niña event in the Pacific Ocean.

Rainfall was generally above average in northern NSW, particularly along the northeast coast, with the wettest January since 1951 at Tweed Heads and since 1974 at Grafton and Murwillumbah. Rainfall was also above average along the western border, with Broken Hill (Patton St) recording 158.6 mm, the wettest January since 1974. In comparison, rain was below average in parts of southern NSW. The Murray-Darling Basin recorded 82.5 mm compared to the historical average of 55.1 mm, also the wettest January since 1996.

There were several major rain events in northeastern NSW during the month. Between the 16th and 18th, an East Coast Low embedded in a low pressure trough off the coast triggered moderate to heavy falls along the north coast, reaching 105 mm at Boat Harbour (Rous River) on the 17th. This was followed by a major sustained rain event between the 23rd and 27th, as a slow-moving high pressure system directed persistent moist easterly winds into the state, enhanced by an upper level trough. Falls were heaviest along the coast, reaching 275 mm at Boat Harbour (Rous River) on the 25th, with widespread areas reaching 100 mm for several consecutive days, triggering coastal flooding. Rain also extended well into northwestern NSW, particularly on the 28th and 29th as the system moved offshore. However, few records were broken for daily rainfall, with similar falls in several recent years at affected locations.

Temperature

NSW recorded a statewide average maximum temperature of 30.9 °C during January, 0.7 °C below the historical average. This is the first time NSW has recorded below average temperatures in January since 2000, which was 1.5 °C below average. Temperatures were generally below average in the northeast of the state and above average in the south, consistent with the pattern of rainfall anomalies during the month.

Minimum temperatures in NSW during January were 0.05 °C above the historical average of 17.7 °C, but still the coldest January since 2002, following an extended warm spell in recent years. Temperatures were generally below average in eastern NSW but above average in the west, with most areas within 1 °C of average. Lord Howe Island was also abnormally cold, with the coldest January night and mean minimum temperatures since records began in 1989.

NSW mean temperatures were consequently 0.3 °C below average, the first below average January since 2000.

Temperatures were particularly cool during a cold snap on the 11th, which was the coldest January day on record for Thredbo, and consequently the lowest temperature on record for NSW in January. This was followed by an unusually cold night on the 12th, with large parts of the state more than 8 °C below average and the coldest night on record at 16 stations including Parkes and Canberra Airport. For more information on this event please see Special Climate Statement 36.

Other phenomena

A heavy rain event between the 23rd and 27th of January along the north coast of NSW triggered flooding in the Northern Rivers, particularly along the Tweed. The SES received more than a thousand Requests for Assistance during this week, including 50 flood rescues, particularly in the Tweed area. More than 4000 people were evacuated from a number of towns during the event, while more than ten thousand people were isolated for some period, including areas of Bellingen, Thora, Darkwood, upper Macleay and Mullumbimby.

Heavy rainfall also triggered flash flooding in Broken Hill on the 27th, with three flood rescues performed in the area, in addition to wind gusts of up to 96 km/hr. Some rural communities along the Darling river system remained isolated during January following the continuation of flooding from December.

Notes

A Monthly Climate Summary is prepared to list the main features of the weather in New South Wales using the most timely and accurate information available on the date of publication; it will generally not be updated. Later information, including data that has had greater opportunity for quality control, will be presented in the Monthly Weather Review, usually published in the fourth week of the month.

This statement has been prepared based on information available at
10 am on Wednesday 1 February 2012.
Some checks have been made on the data, but it is possible that results will change
as new information becomes available.

Averages are long-term means based on observations from
all available years of record, which vary widely from site to site.
They are not shown for sites with less than 20 years of record, as they cannot then be calculated reliably.
The median
is sometimes more representative than the
mean
of long-term average rain.

The Rank indicates how rainfall this time compares with the climate record for the site,
based on the
decile ranking
(very low rainfall is in decile 1, low in decile 2 or 3,
average in decile 4 to 7, high in decile 8 or 9
and very high is in decile 10).
The Fraction of average shows how much rain has fallen this time as a
percentage of the long-term mean.